Modern integrated circuits chips such as Dynamic Random Access Memory (DRAM) chips have many different voltages that have to be generated on the chip by a plurality of generators. Each of the generators is manufactured to provide a specific voltage to the integrated circuit. However, due to variations in the manufacturing process the actual voltage provided by each generator can initially vary outside of an acceptable range. To correct these variations the voltage generators on integrated circuits often are trimmed to provide an internal voltage within the acceptable range.
FIG. 1 shows a conventional scheme for trimming the voltage of a voltage generator on an integrated circuit chip 100. Integrated circuit chip 100 includes a voltage generator 102, a test-mode controller 104, and a test-pad 106. The voltage generator 102 produces an internal voltage 108 from an external voltage 110. The voltage generator can include, for example, a voltage divider or voltage pump that produces an internal voltage 108 that is less than or greater than the external voltage 110. The internal voltage 108 can be distributed to an integrated circuit via electrical connection 112. The integrated circuit can include, for example, a memory array. The internal voltage 108 is also distributed to a test-pad 106 via electrical connection 114.
To trim the internal voltage, the internal voltage 108 is distributed to an external tester 118 through an electrical connection 116 made between the external tester 118 and test-pad 106. The external tester 118 determines the value of the internal voltage 108. If the internal voltage 108 needs to be trimmed, the external tester 118 sends tester signal 120 to test-mode controller 104. Test-mode controller 104 translates the tester signal 120 into control signals 122 for adjusting voltage generator 102. The adjustments to voltage generator 102 modifies the internal voltage 108 produced by the voltage generator 102.
The internal voltage 108 is continually modified until it is within a predetermined range. Once the internal voltage is within the predetermined range, the trim adjustments made to voltage generator 102 can be made permanent by programming the status of the control signals on the integrated circuit accordingly. Permanent programming can be accomplished, for example, by the setting of non-volatile storage elements residing on the integrated circuit. These storage elements can include, for example, laser fuses (which are fuses that are programmed by an external laser beam) or electrical fuses that are programmed by an electrical signal.
In the conventional scheme for trimming the internal voltage of an integrated circuit chip an external tester is used to measure each internal voltage and then to relay this information back to the chip. Because the external tester must typically measure each voltage individually, it is difficult to trim multiple internal voltages simultaneously without using a complicated external tester. Since modern integrated circuit chips, like DRAMs, often include multiple internal voltages a voltage generator scheme which can allow multiple internal voltages to be simply and efficiently trimmed simultaneously is desirable. Also, in the conventional scheme, the simultaneous testing of multiple integrated circuit chips is limited because the external tester can not typically share the control and measurement signals for more than one chip. Each voltage on each chip must be measured independently. Furthermore, the trimming information must be supplied to each chip individually. Accordingly, a voltage generator scheme which allows for the simultaneous trimming of multiple integrated circuits chips is desirable to increase the efficiency of the trimming process.